1. Field of the Invention
The present invention relates to a method and apparatus for reaming or enlarging a horizontal or gently inclined pilot hole. Here, the pilot hole is a drilled hole extending in a straight line or in a curved line and having a bore diameter of approximately 100-300 mm which is drilled in the earth.
2. Description of the Prior Art
A drilling machine which arranges a plurality of hydraulic-hammer driven drill bits relative to a drilling cross section has been marketed. The drilling machine is suitable for drilling a hole having a bore diameter of approximately 250 mm-1000 mm. In this drilling machine, a plurality of drill bits which are arranged on a drilling surface are respectively driven by hydraulic hammers and the whole drilling machine is slowly rotated by means of a drill pipe so as to perform drilling. The drilling machine, for example, does not require a large torque for rotating the whole drilling system compared to a rotary drilling machine which performs drilling by rotating the drilling machine per se so that the drilling machine may be made compact while assuring the powerful drilling performance. That is, the rotational force sufficient to shift the contact surface of the drill bits is transmitted by means of the drill pipe and it is unnecessary to produce the rotational torque contributed to drilling. Since the drilling is performed by driving the compact and powerful hydraulic hammers which perform the impact drilling, the drilling machine exhibits the high performance. Although the drilling machine can perform the highly efficient drilling with the use of compact drill bits and a small amount of pressurized liquid, the diameter of the drilled hole is large so that there exists a drawback that a large amount of water and/or highly viscous drilling fluid becomes necessary to discharge cuttings(drilled rock powder). Accordingly, conventionally, it has been a common knowledge that such drilling machine may not be applicable to the reaming of horizontal or gently inclined pilot holes. Here, a gently inclined hole means a hole having an inclination angle of 30xc2x0 or below.
It is an object of the present invention to overrule such a conventional knowledge and to provide a method and apparatus which use the drilling machine provided with a plurality of hydraulic hammer driven bits as a reaming machine for reaming a horizontal or gently inclined pilot hole at high efficiency.
It is another object of the present invention to get a larger diameter reamed hole in one process using very less amount of water assumption to discharge cuttings.
The present invention has been made to solve the above-mentioned problems and provides a method for reaming a pilot hole characterized in that, in reaming a horizontal or gently inclined pilot hole, a reaming machine which arranges a plurality of hydraulic hammer driven drill bits in parallel on a reaming cross section is used, and a drill pipe is connected to a trailing-end side or/and a leading-end side of the reaming machine, and the reaming is performed while discharging cuttings through the pilot hole or/and the drill pipe. In view of the difficulty of discharging cuttings through a reamed hole of a large diameter, the reaming apparatus of this type has not been considered to be suitable for reaming the horizontal or the gently inclined pilot hole. However, the present invention has overruled such a conventional common knowledge and has made it possible to ream the horizontal or gently inclined pilot hole. The most outstanding feature of the present invention lies in adopting following methods (a)-(d) for discharging cuttings.
(a) Cuttings is discharged through the pilot hole.
(b) Cuttings is discharged through the drill pipe mounted on the leading-end side of the reaming machine.
(c) Cuttings is discharged through the pilot hole and the drill pipe mounted on the leading-end side of the reaming machine.
(d) Cuttings is discharged through the drill pipe mounted on the trailing-end side of the reaming machine.
The present invention is characterized by the realization of the transportation and the discharge of cuttings with a little amount of water by adopting any one of the above-mentioned means which can increase the flowing speed of cuttings by making the cuttings pass through a discharge passage of a narrow cross section.
The apparatus which can suitably carry out the above-mentioned method according to the present invention is an apparatus for reaming a pilot hole which is characterized by including a reaming machine which arranges a plurality of hydraulic hammer driven drill bits in parallel and drill pipes which are connected to front and rear portions of the reaming machine and further including a seal which is mounted on an outer periphery of the reaming machine for sealing a portion of the reaming machine extending between a drill-bit side front face and a rear side of the reaming machine. When this apparatus is of the type in which the rear-end side drill pipe of the reaming machine propels the reaming machine, the apparatus is an apparatus for reaming a pilot hole which is provided with the drill pipe for pushing the reaming machine from the rear side and simultaneously supplying pressurized water at a trailing-end side of the reaming machine and the pilot hole or/and the front-end side drill pipe is used as cuttings discharge passage.
On the other hand, when the apparatus is of the type in which the front-end side drill pipe of the reaming machine tows the reaming machine, the apparatus is preferably an apparatus for reaming a pilot hole which is provided with the drill pipe for towing the reaming machine in the frontward direction and simultaneously supplying pressurized water at the front end side of the reaming machine, connects the drill pipe or other pipe to the trailing-end side of the reaming machine and uses the trailing-end side drill pipe or/and other pipe as cuttings discharge passage. Here, the trailing-end side pipe is not required to transmit pressure and torque and hence, such a pipe is not limited to the drill pipe.
Further, the apparatus may be an apparatus for reaming a pilot hole in which the apparatus is provided with the drill pipe which tows the reaming machine in the frontward direction and simultaneously supplies pressurized water at the leading-end side of the reaming machine and uses the pilot hole as cuttings discharge passage without connecting the drill pipe or other pipe to the trailing-end side of the reaming machine.